The present invention relates generally to disposable food contact articles and more specifically to a disposable food serving bowl formed of a high modulus, mineral-filled polyolefin sheet and more preferably mineral-filled sheet.
Disposable articles are commonly formed with a curled lip to impart strength to a cup, canister, or carton for example, as is seen in U.S. Pat. No. 5,184,995 to Kuchenbecker. The curl tends to give the article a utilitarian look and feel, not necessarily optimally aesthetically pleasing; especially for disposable articles which can be re-used on multiple occasions such as plastic articles.
There is shown in the U.S. Pat. No. 4,578,296 of Miyazaki et al. a thermoformed article manufactured from filled polyolefin sheet. The polyolefin resin composition includes from 30 to 80 percent of resin, from 19 to 69 percent by weight talc and from 1 to 10 percent by weight titanium dioxide. An article formed from the sheet typically includes a curled lip or a severely downwardly projecting outer lip. Note column 9, line 49 through column 10, line 38.
In accordance with the present invention, there are provided disposable serving bowls without a curled or severely downturned flange, which features are undesirable in terms of aesthetic qualities and brittleness.
The invention is described below with reference to the attached figures which show preferred shapes and relative dimensions.
The bowls of the present invention include in a preferred embodiment a plastic bowl with a four-radius profile which balances the need for increased rigidity (strength) and rim stiffness (sturdiness) per given material weight/cost. The ergonomic rim profile provides for ease of holding and carrying, consumer friendly shape denoting Permanentware qualities, without the negative side effect of brittleness encountered when using high modulus/stiffness construction materials. The four-radius disposable plastic bowl design has a curvilinear rim surface onto which patterning can be applied for visual, tactile and strength purposes. The bowls were rigid and strong, not brittle, during use even with the high modulus/stiffness mica-filled polypropylene (PP) plastic material.
Bowls produced with other shapes were rigid but often failed by brittle cracking in the flange and downturn areas. The stresses generated in the flange and downturn areas by deflection of the product during use apparently exceeded the highly filled material strength resulting in failure. It is possible that imperfections on the product""s trimmed edge may contribute to brittle cracking by providing failure initiation points for the notch sensitive, highly filled materials preferably used in accordance with the invention.
It was discovered that plastic bowls described in this invention disclosure still had exceptional strength per material weight, but also significantly reduced brittle cracking with the highly filled nonhomogeneous materials. The four-radius design, for example, would not build up the high stress levels during deflection even with trimmed edge imperfections and was less prone to brittle cracking.
Bowls having a circular configuration as illustrated employ the four-radius plastic bowl design. The plastic bowls may also be square or rectangular in shape having angular comers. Further, additional plastic shapes such as triangular, multi-sided, polyhexal, etc. are contemplated.
It will be appreciated that a salient feature of the inventive bowls is the smooth profile as described herein. In general, the transitions between the center, sidewall and flange of the bowl are kept free of bends or curves so that mechanical stresses are not concentrated beyond the ability of the material to withstand them. In addition to being operative to avoid undesirable stress regions, the profile is flowing in appearance and provides a pleasing, ergonomic hand feel.
In general, the invention is directed to disposable food serving bowls formed of a polyolefin, mineral-filled sheet and having a characteristic diameter as well as a substantially planar central portion, a sidewall portion and a flange portion. For a circular article such as a circular bowl, the characteristic diameter is simply the diameter of the bowl as the term is ordinarily employed, i.e., the distance through the center between opposing outer edges of the flange. For non-circular articles, the characteristic diameter is the average distance through the center between opposing outer edges of the flange. Thus, for a rectangular article the characteristic diameter is the average of the shorter side and the longer side, for an oval article the characteristic diameter is the average of the minor axis length and the major axis length of the oval and so forth.
There is provided in a first aspect of the present invention a disposable food serving bowl formed of a mineral-filled polyolefin sheet including a substantially planar central portion, a sidewall portion and a flange portion having a characteristic diameter, D, measured in inches, as well as a characteristic volume, V, measured in U.S. fluid ounces. As used herein, the term xe2x80x9cfluid ouncesxe2x80x9d refers to U.S. fluid ounces or 1.805 cubic inches. It will be appreciated that while a nominal 20 fluid ounce bowl is specifically exemplified, such a bowl may have a slightly greater xe2x80x9cfull to the brimxe2x80x9d capacityxe2x80x9d of 23 fluid ounces or more to allow for slight changes in orientation during movement or use. Likewise, a nominal 20 ounce bowl could contain less than 20 fluid ounces (say 19 ounces or so) if filled to a level at the start of the flange region.
The sidewall portion extends outwardly and upwardly from said central planar portion; while the flange portion extends outwardly from the sidewall portion and is characterized by an outer arcuate rim portion with a radius of curvature subtending an outermost arc. The outermost rim portion also defines the outer edge of the bowl and has a downwardly projection terminus. The radius of curvature of said outermost arc in inches is from about (V/20)⅓xc3x970.15 to about (V/20)⅓xc3x970.35. Preferably, the radius of curvature of the outermost arc is from about (V/20)⅓xc3x970.2 to about (V/20)⅓xc3x970.3. The outermost arc typically extends over a total angle of from about 60 to about 85 degrees, and most preferably over an angle from about 70 to about 75 degrees. The outermost arc typically also extends from a vertical line at its apex or peak downwardly through an angle of from about 35 to about 55 degrees. More preferably, the outermost arc extends from a vertical line at its apex or peak downwardly through an angle of from about 40 to about 50 degrees.
The bowls typically have a wall thickness of from about 10 to about 80 thousandths of an inch (mils) and preferably from about 15 to about 25 mils. The most preferred materials are crack resistant, filled polypropylenes consisting essentially of from about 40 to about 90 percent by weight of a polypropylene polymer, from about 10 to about 60 percent by weight of a mineral filler, from about 1 to about 15 percent by weight polyethylene, from about 0.1 to about 5 weight percent titanium dioxide and optionally including a basic organic or inorganic compound comprising the reaction product of an alkali metal or alkaline earth element with carbonates, phosphates, carboxylic acids as well as alkali metal and alkaline earth element oxides, hydroxides, or silicates and basic metal oxides, including mixtures of silicon dioxide with one or more of the following oxides: magnesium oxide, calcium oxide, barium oxide, and mixtures thereof.
Preferably, the basic organic or inorganic compound comprises calcium carbonate and the calcium carbonate is present in an amount of from about 5 to about 20 weight percent. Polyethylene is usually present from about 2.5 to about 15 percent by weight; however, typically from about 4 to about 5 weight percent is more preferred.
Titanium dioxide is generally present from about 0.1 to about 3 weight percent; more typically, titanium dioxide is present from about 0.25 to about 2 percent by weight. Most preferably, titanium dioxide is present in an amount of at least about 0.5 percent by weight.
Generally, the bowls have a wall caliper of from about 10 to anywhere from about 50 to about 80 mils; while a wall caliper of from about 15 to about 25 mils is more typical. A preferred mineral filler is mica and a preferred polypropylene polymer is isotactic polypropylene which has a melt index of from about 0.3 to about 4. Most preferably, the isotactic polypropylene has a melt flow index of about 1.5.
Particularly preferred polyethylenes include HDPE and LLDPE.
In another aspect of the invention there is provided a disposable food serving bowl formed of a mineral-filled polyolefin sheet comprising a planar central portion, a sidewall portion and a flange portion, the sidewall portion extending outwardly and upwardly from the central planar portion; and the flange portion extending outwardly from said sidewall portion and being characterized by an outer arcuate rim portion with a radius of curvature subtending an outermost arc. The outermost rim portion defines the outer edge of said bowl which has a downwardly projecting terminus. The radius of curvature of said outermost arc is from about 0.15 inches to about 0.35 inches. The radius of curvature of the outermost arc is typically from about 0.2 to about 0.3 inches, while the polyolefin is typically polyethylene, polypropylene or mixtures thereof.
In still yet another aspect of the present invention there is provided a disposable food serving bowl formed from a mineral-filled polyolefin sheet with a characteristic volume, V, in (U.S.) fluid ounces, having a substantially planar center portion; a first sidewall portion extending outwardly from said center planar portion, said first sidewall portion being upwardly convex and subtending a first arc with a first radius of curvature; a second sidewall portion joined to said first sidewall portion, and extending outwardly therefrom, said second sidewall portion being downwardly convex, subtending a second arc with a second radius of curvature; a third sidewall portion joined to said second sidewall portion and extending outwardly therefrom, said third sidewall portion being downwardly convex, subtending a third arc with a third radius of curvature; and, a fourth rim portion joined to said third sidewall portion and extending outwardly therefrom, said fourth rim portion being downwardly convex subtending a fourth arc having a fourth radius of curvature; wherein said fourth radius of curvature, in inches, is from about (V/20)⅓xc3x970.15 to about (V/20)⅓xc3x970.35. As noted above, the fourth arc passes through a vertical maximum and continues downwardly through an angle of from about 35 to about 55 degrees in a downwardly convex manner.
Typically, the second radius of curvature is greater than the third radius of curvature and the third radius of curvature is greater than the first radius of curvature which, in turn, is greater than the fourth radius of curvature.
The first arc and the second arc are similar or equivalent in length and both of which are greater in length than the third arc. The third arc is typically greater in length than the fourth arc.
As will be seen from the following description, the first arc extends over an angle of from about 50 to about 85 degrees, the second arc extends over an angle of from about 5 to about 9 degrees, the third arc extends over an angle of from about 25 to about 40 degrees, while the fourth arc extends over an angle of from about 60 to about 85 degrees; and from about 35 to about 55 degrees from its vertical maximum or apex.
Various details will become more understood by reference to the attached Appendix, drawings and detailed description which follows.